I am a frequent traveller who enjoys getting my passport stamped (when I have pages, anyway). On a visit to Liechtenstein, I received a stamp from Liechtensteinish officials (purely for souvenir purposes since there isn't any actual border control in the principality).
I was surprised to recently see that Wikipedia claims (without citation):
Some travellers "collect" immigration stamps in passports, and will choose to enter or exit countries via different means (for example, land, sea or air) in order to have different stamps in their passports. Some countries, such as Liechtenstein, that do not stamp passports may provide a passport stamp on request for such "memory" purposes. However, such memorial stamps can preclude the passport bearer from travelling to certain countries. For example, Finland consistently rejects what they call 'falsified passports', where travelers have been refused visas or entry due to memorial stamps and are required to renew their passports.
Will my stamp from Liechtenstein really get me denied access to Finland? I'm sceptical of the claim, as its uncited, but then again, many countries have odd border rules.